Liquid crystal display devices have become widely used for consumer application to industrial application, such as liquid crystal televisions, cellular phones, personal computers, etc. These products have a relatively long lifetime of several years to several tens years, and liquid crystal materials used in liquid crystal display devices are required to have high stability in order that the display devices normally operate for the lifetime. A typical index for stability of liquid crystal materials is a resistivity value. In order that liquid crystal display devices normally operate, it is necessary for liquid crystal materials used in the display devices to have a sufficiently high resistivity value and to be suppressed from degrading over time.
In order to improve stability of liquid crystal materials, many researches have been conducted. A typical example thereof relates to a method of bringing a liquid crystal material into contact with silica gel or alumina to remove moisture, organic ions, inorganic ions, and the like from the liquid crystal material, thereby enhancing a resistivity value (Patent Literatures 1 and 2).
However, some compounds constituting liquid crystal materials may cause reaction such as dimerization or decomposition by contact with silica gel or the like, resulting in a decrease in purity and a decrease in resistivity value with the decrease in purity. This tendency is particularly high in compounds having an alkenyl group or a polymerizable group in a side chain. Therefore, there is desire for a simple practical method for achieving a high resistivity value without deterioration in compounds constituting liquid crystal materials, but a specific solving method has not yet been reported.